Along with the technical evolvement and emerging data services, such a scenario may occur in later releases of the Long Term Evolution-Advance (LTE-A) system that a User Equipment (UE) is configured to operate while being served by a plurality of eNBs (i.e., dual connectivity).
For example, a UE is configured with a Master Evolved NodeB (MeNB) and at least one Secondary eNB (SeNB), where in the dual connectivity application scenario, at least an S1-MME (MME stands for a Mobility Management Entity, and S1 represents an S1 interface to the MME) is terminated at the MeNB, so the MeNB can be regarded as a mobile anchor; and the SeNB is responsible for providing the UE with an additional radio resource in addition to the MeNB, from the prospective of a core network.
In the dual connectivity scenario, frame structures applied to cells and/or carriers scheduled by different eNBs may or may not be the same. For example, a Frequency Division Duplex (FDD) frame structure is applied to the respective carriers scheduled by the different eNBs for the UE, or a Time Division Duplex (TDD) frame structure is applied to the respective carriers scheduled by the different eNBs for the UE (where TDD uplink/downlink configurations applied to the respective carriers scheduled by the different eNBs may or may not be the same), or an FDD frame structure is applied to respective carriers of the UE in one frequency band, and a TDD frame structure is applied to respective carriers of the UE in another frequency band.
In the dual connectivity scenario, the plurality of eNBs with which the UE is connected schedule their respective sets of downlink carriers separately, where data can be scheduled and transmitted to the UE in the following three options:
In a first option, bearers of the MeNB are routed directly to the MeNB from a gateway (e.g., a Serving Gateway (S-GW)); and bearers of the SeNB are routed directly to the SeNB from the gateway, that is, the bearers of the SeNB need not be routed through the MeNB, as illustrated in FIG. 1;
In a second option, bearers of the MeNB are routed directly to the MeNB from a gateway; and bearers of the SeNB are firstly routed to the MeNB from the gateway, and then all the bearers are offloaded by the MeNB to the SeNB, that is, the bearers of the SeNB are not separated, as illustrated in FIG. 2; and
In a third option, bearers of the MeNB are routed directly to the MeNB from a gateway; and bearers of the SeNB are firstly routed to the MeNB from the gateway, and then a part of the bearers are offloaded by the MeNB to the SeNB, whereas the remaining bearers are still transmitted at the MeNB side, that is, the bearers of the SeNB are separated, as illustrated in FIG. 3.
At present the UE operates while being served by only one eNB, where Power Control (PC) parameters thereof are configured by the eNB, and the UE is configured with only one set of PC parameters for calculating transmit power of uplink channels including a Physical Uplink Control Channel (PUCCH), a Physical Uplink Shared Channel (PUSCH), a Sounding Reference Signal (SRS), a Physical Random Access Channel (PRACH), etc., where the set of PC parameters are determined for a transmission characteristic between the UE and the one eNB, and also Path Loss (PL) measurement is made only for the one eNB.
Moreover a PUCCH is transmitted only over a primary carrier, and there is only one PUCCH; and for a PUSCH, there is only one PUSCH over which transmission of uplink control information can be carried. Thus if the UE is limited in power, then the priority of the PUCCH will be defined higher than the priority of the PUSCH over which uplink control information is carried, and the priority of the PUSCH over which uplink control information is carried will be defined higher than the priority of a PUSCH over which no uplink control information is carried, so that transmit power of the uplink control information will not be reduced so as to be transmitted reliably.
At present in the dual connectivity scenario, in order to feed back uplink control information corresponding to a plurality of eNBs concurrently over one uplink carrier, the UE may need to transmit a plurality of PUCCHs or PUSCHs over which uplink control information is carried, concurrently over the one uplink carrier, or transmit uplink control information corresponding to a plurality of eNBs, concurrently over one PUCCH or PUSCH, and since there may be different frequencies at which the different eNBs operate, and different propagation paths and transmit channel states between the UE and the different eNBs, the existing solutions to PC parameter configuration, PL measurement, and power reduction will not be applicable any longer in this situation.
In summary, there has not been so far a corresponding solution to uplink power control on a UE transmitting in the uplink in the dual connectivity scenario.